The invention relates to a driving mechanism comprising a spindle, which is supported in at least one sleeve rotatable by means of a motor, is rotatable and displaceable with respect thereto and is provided with at least one helical guide, with which the sleeve is in engagement by means of a number of roller members.
The invention further relates to a manipulator comprising a driving mechanism of the kind mentioned in the opening paragraph.
The European patent application Ser. No. 1-0188863 discloses a manipulator or robot comprising a driving mechanism of the kind described hereinbefore. With the known driving mechanism, which is used in the said manipulator for displacing an end effector or gripper, a translation of the spindle is obtained via a number of balls (roller members) guided in an inner duct which is constituted by the helical guide of the spindle and a helical inner groove of the sleeve, which is adjoined by an outer duct, which is constituted by a helical outer groove of the sleeve and a cylindrical inner wall of a housing, in which the sleeve is journalled radially and axially. The sleeve acting as a nut is secured to a first pulley, which is coupled via a toothed belt to a first motor. A rotation of the spindle in the known driving mechanism is obtained by means of a further sleeve, which is arranged to surround the spindle and is provided with three axial grooves, which adjoin three corresponding axial grooves in the spindle so that a cage is formed for a number of balls which transmit a torque from the further sleeve to the spindle. The further sleeve is driven by a second motor via a second pulley and a second toothed belt. A simultaneous translation and rotation of the spindle is obtained by activating both the first and the second motor. A driving mechanism of the kind known from European patent application Ser. No. 1-0188863 is further described in European patent application Ser. No. 1-0162980. In the driving mechanism according to the last-mentioned European patent application, use is made of a sleeve acting as a nut and having a helical guide, which corresponds to the helical guide on the spindle.
A disadvantage of the known driving mechanisms is that due to the large number of contact points between the sleeve and the spindle a kinematically overconstrained construction is obtained, which can operate only with a sufficient amount of clearance between the sleeve and the spindle. The attainable positioning accuracy of the driving mechanism is thus comparatively low. In the case in which the driving mechanism is used in a manipulator, the said disadvantage becomes more pronounced because of the required repetition accuracy in manipulators. A further disadvantage of the known driving mechanism resides in the differences in construction of the mechanism for the translatory and rotary movement, respectively, of the spindle. This leads not only to a comparatively large number of component parts and a comparatively large mass inertia, but also requires a comparatively high power of the two motors.